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July 19, 2011 (Paris) -- One in three retired NFL football players appear to have mild cognitive impairment (MCI), researchers report.

"Cognitive impairment seems to be more prevalent in retired American football players than in the general population that age, where you do not see rates anywhere approaching 35%," says study head Christopher Randolph, PhD, clinical professor of neurology at Loyola University Medical Center in Chicago.

The findings are preliminary. And not every football player is destined to develop memory loss or other cognitive problems, says William Thies, PhD, scientific director of the Alzheimer's Association.

Also, current players may be at less risk than in the past, he tells WebMD. NFL rules now require that players with symptoms of a concussion be cleared by a neurologist before they can return to play.

But the findings suggest that mild, repeated blows to the head -- like the kind suffered by many players during their careers -- may predispose people to dementia. That challenges the view that only moderate or severe brain injuries that render one unconscious pose a danger.

The findings were presented here at the Alzheimer's Association International Conference.

Football Players and Head Trauma

About 1.7 million Americans suffer brain injuries each year, according to the CDC.

Head injuries among football players have grabbed headlines in recent months. Earlier this month, Baltimore Colts tight end John Mackey died after being diagnosed with dementia. The autopsy of former Chicago Bears safety Dave Duerson, who killed himself in February at age 50, showed evidence of traumatic brain injury.

The new findings come from a follow-up study to the researchers' 2005 study showing that retired football players appeared to be at increased risk for mild cognitive impairment and Alzheimer's disease.

The researchers hypothesized at the time that "this might be due to repeated concussions or the cumulative effects of repetitive head trauma," Randolph tells WebMD.

Other recent studies have shown that the average college football player incurs more than 1,300 blows forceful enough to lead to permanent injury every season, he says.

Memory Testing

The new study involved 633 retired NFL players -- age 50 or older -- who responded to a survey about their general health in 2001 and a second survey focusing on memory issues in 2008.

The latter survey included the AD8 screening tool, which was completed by the men's spouses. Scores of 2 or greater suggests substantial cognitive impairment.

A total of 513 of the returned surveys included a completed AD8 test. Results showed that 35% of the retirees had a score of 2 or greater, which "we found startling, particularly because the men were relatively young, with an average age of 61 years," Randolph says.

Another 53% of the former NFL players had a score of 0, or no cognitive impairment, on the test; 12% had a score of 1, indicating mild memory loss and other cognitive problems.

Forty-one of the players whose AD8 scores indicated cognitive impairment then agreed to be further evaluated at the University of North Carolina at Chapel Hill Center for the Study of Retired Athletes. As part of a clinical trial, they were compared with 41 healthy NFL retirees of similar age, education, and race, and 81 older patients with confirmed MCI who had not played football.

All were given a test called the Repeatable Battery for the Assessment of Neuropsychological Status (RBANS), a tool that Randolph himself developed to evaluate patients' language and visual/spatial skills, attention span, and immediate and delayed memory.

"The profile of cognitive impairment [seen in the retired football players] on RBANS was very similar to that of patients with clinically diagnosed MCI," Randolph reports.

He cited as an example their scores on a question dealing with delayed memory -- the ability to recall something from the past. Higher scores indicate better performance.

The MCI patients had an average score of 75, which put them in about the fifth percentile of normal for their age, he says. Retired NFL players with suspected cognitive impairment had average scores in the mid-80s, which falls into about the 15th percentile of normal. The healthy retirees had scores of about 100, which is normal for their age, he says.

Despite their below average scores on RBANS, the retired NFL players with suspected cognitive impairment "were still highly functioning, with an average IQ of 106," Randolph says.

The findings should be considered preliminary, he says. Many retired football players have other conditions, such as high blood pressure, obesity, and diabetes that are risk factors for cognitive impairment.

While there are competing hypotheses regarding how repetitive head injury might raise the risk of cognitive disorders later in life, Randolph says he believes cell loss chips into our cognitive reserve -- the extra capacity that you have to accomplish tasks mentally. You can think of cognitive reserve as your brain's savings account to reach into in times of hardship; we all have some reserves, some more than others.

These findings were presented at a medical conference. They should be considered preliminary as they have not yet undergone the "peer review" process, in which outside experts scrutinize the data prior to publication in a medical journal.